Psychiatric comorbidity as predictor of costs in back pain patients undergoing disc surgery: a longitudinal observational study

Table 3 Predictors of direct, indirect and total costs; base case scenario

Parameter	Direct costs	Standard error		Indirect costs	Standard error		Total costs	Standard error
Constant	4,762	559	***	3,998	768	***	8,757	976	***
Diagnosis	478	128	***	6.52	231		509	280
Psychiatric comorbidity	664	265	*	808	376	*	1,469	528	**
T1	−2,456	130	***	3,028	235	***	571	291	*
T1 x psychiatric comorbidity	−578	350		−1,248	600	*	−1,829	783	*
T2	−4,634	164	***	−2,370	288	***	−6,996	370	***
T2 x psychiatric comorbidity	72	517		1,333	833		1,355	1,089
Chronic medical disease	467	155	**	951	249	***	1,417	317	***
Number of previous disc surgeries	503	141	***	1,142	167	***	1,645	228	***
Age (centralized to mean)	−6.28	7.66		48	14	***	41	17	*
Gender (ref: female)	−354	130	**	1,572	189	***	1,203	246	***
Being married	95	137		363	273		462	333
ISCED educational level 3 (ref ≤ 2)	451	401		−280	634		132	762
ISCED educational level 5 (ref ≤ 2)	367	414		−790	665		−460	803
Living situation: with partner (ref: alone)	−325	231		87	359		−180	440
Living situation: others (ref: alone)	−52	458		344	919		374	1,060
Number of children	64	59		−249	102	*	−196	128
Private health insurance (ref: statutory health insurance)	−57	139		−759	279	**	−799	340	*
Being not employed (ref: being employed)	238	196		−4,502	331	***	−4,228	409	***
Model statistics
R2 within	0.55			0.42			0.46
R2 between	0.33			0.28			0.26
R2 overall	0.46			0.34			0.36

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